1. Field of the Invention
The present invention generally relates to compressive force measurement. More particularly, the invention provides a method and apparatus for measuring the nip loading force applied compressively between two process rolls.
2. Description of the Prior Art
Numerous web handling processes such as papermaking utilize compressive nip forces as are obtained from two oppositely loaded rolls. When the process requires extremely high nip loads, the rolls are mounted on massive bell cranks or other mechanical means for multiplying the force of hydraulic or pneumatic loading struts.
These mechanical force multiplying devices operate as matched pairs with each assembly of the pair supporting a respective roll axis end. When these mechanical load multipliers are correctly aligned, the fluid pressure applied to the loading struts is directly proportional to the radial nip load. However, slight misalignment or journal wear may cause large resulting nip load differences: notwithstanding identical fluid pressure applied to the respective loading struts. Consequently, it is occasionally necessary to directly measure the load asserted within such a roll nip to verify or calibrate the normal fluid pressure system.
When such test loading is done, it is essential that the subject roll nip be as close to the normal operating position as possible since small relative angle differences between the several links in the force multiplying mechanism result in large resulting load differences. For this reason, process roll nips respective to extremely thin materials such as paper or foil represent a unique difficulty.
It is therefore, an object of the present invention to provide a method and apparatus capable of measuring maximum process nip loads within one inch of a closed nip position.
Another object of the invention is to provide a test load cell having an extremely low sectional profile.